As others have beaten me to... Yes, one acre is plenty big enough, but not nearly enough if you don't want it chewed up & to be feeding out full time. Therefore, not likely that the horse will end up exercising much in this area either, unless you implement a setup that encourages more - eg. 'laneways' with hay, water, shelter at different areas.
And horses do survive on their own, but they're herd animals who don't like living alone & this can become problematic for their health & wellbeing. Not to say you need 2 percherons - could always have a mini for company, or even a goat or such.
As for shelter, if there is adequate tree coverage, especially as windbreaks, &/or you rug the horse in bad weather, this will probably be fine until your barn is built. Otherwise a lean-to that will protect her from wind & rain when she feels the need is fine. Can get by with a 2 sided affair.